1. Field of the Invention
The invention relates generally to a storage system and, more particularly, the invention relates to managing shadow copies.
2. Description of the Related Art
The server operating system by MICROSOFT Corp. of Redmond, Wash. called XP/.NET Server contains an integrated application for making shadow copies. Such shadow copies are also known as “snapshots” and can either be hardware or software copies depending on the snapshot program being used. Common snapshot programs include the previously-mentioned XP/.NET Server snapshot program by MICROSOFT, the TIMEFINDER snapshot program by EMC Corp. of Hopkinton, Mass., and the EVM snapshot program by COMPAQ Computer Corp. of Houston, Tex.
Generally, when a shadow copy is taken by a machine, a new logical volume is created on the machine itself that is an exact image of the original volume. All of the data of the original volume including how application and other software processes recognize and interact with the data is also preserved.
While changes can continue to occur on the original volume, the new volume is a static, point-in-time view of the data. Since shadow copies exist on a user's workstation, or an accessible network machine, the shadow copies provide the ability to have multiple versions of data ready for recovery at a moment's notice. Shadow copies enable minimal restore time, and therefore minimal downtime while the restore operation is being performed, since there is no need to mount external media, such as tape or optical media, to stream data back therefrom during such a restore. This is because the shadow copies are stored on the machine and not on external media.
Although shadow copying offers quick storage and recovery capability, the snapshots are stored on relatively expensive media, such as a fast hard drive, or on a redundant array of independent disks (“RAID”) system. RAID refers to a set of two or more ordinary hard disks and a specialized disk controller. The RAID system copies data across multiple drives, so more than one disk is reading and writing simultaneously. Fault tolerance is achieved by mirroring, which duplicates the data on two drives, and parity, which calculates the data in two drives and stores the results on a third. A failed drive can be swapped with a new one, and the RAID controller rebuilds the lost data on the failed drive. Some storage systems copy storages to slower media, such as slow hard drives, tape drives, etc.; however, the downtime associated with a storage and recovery for such systems is increased. Moreover, storage copies are formatted or compressed for optimum utilization of storage media. Restoring such storage copies further require the extra step of unformating or uncompressing the storage copy for use by the computer system. There is therefore a need in the art for a storage system which minimizes the downtime associated with a storage and restore operation while taking advantage of less expensive media.
Additionally, the software products available to create shadow copies, such as the XP/.NET, TIMEFINDER, etc., are not efficiently managed. For instance, administrators in many instances must track shadowed copies, remember which original volume corresponds to particular shadowed copies, what data existed on these volumes, when a copy operation occurred, if a copy should be destroyed, etc. There is therefore a need in the art for a method and system that enables efficient management of shadowed copies.
Additionally, the software products used to make traditional incremental storages monitor changes to volumes at the file level. If a file changes between storages, the entire file is recopied to secondary storage which is inefficient and uses excessive system resources. For example, if two blocks in a 1000 block file changed, all 1000 blocks would be stored again and recopied to secondary storage. Sometimes, these products are used as part of a disaster recovery (“DR”) strategy for a company. Files and other important data are sent via a network for storage at a remote site. If anything happens to the primary site of the company such as a fire or other disaster, the files and data are still preserved remotely. Copying files and data using traditional incremental storages and other current storage methods, however, is inefficient since amounts of information must be copied regardless of how much information has changed since a previous storage. There is thus a need for a method, system, and software that enables more efficient incremental storages.